The following shall constitute a prior art statement in compliance with the guidelines as set forth in 37 CFR Sections 1.56, 1.97 and 1.98.
In producing hydrocarbons from subsea formations, it has become common practice to utilize a drilling template located on the sea floor. Such drilling templates are relatively massive structures incorporating a number of drilling guide tubes disposed in an array within the structure of the template. Patents describing templates of this general nature include U. S. Pat. Nos. 4,174,011, 4,212,562 as well as many others.
Such templates are generally located on the sea floor by attaching them to driven pilings or other anchoring means which have been previously located on the sea floor. A template position is then adjusted to a perfectly horizontal plane so that the vertically disposed drilling guide tubes are as nearly exactly perpendicular to the earth's surface as possible. The drilling of the wells then proceeds from the sea surface from a fixed platform, moored floating platform or a drilling ship located, to as near an extent possible, at a position directly vertically above the drilling guide tubes in the subsea template.
In this manner, a number of production wells are drilled into the hydrocarbon producing formation located below the sea floor. In the drilling of such production wells, it is common to begin drilling a vertical 36 inch diameter hole to a depth of 100 to 300 feet and cementing in a 30 inch conductor within this hole. This is followed by drilling a 26 inch diameter vertical hole below the 30 inch conductor to a depth of 1000 to 1500 feet and cementing in a second conductor of 20 inches in diameter. From the bottom of this conductor, now located at much as 2000 feet below the sea floor, the drilling head is deviated from the vertical so as to penetrate a productive formation at a distance from an adjacent borehole which is greater than the distance separating the drilling guide tubes at the template. Thus, more efficient production of the hydrocarbon fluids from the producing formation is achieved by spreading the producing wells as far apart from each other as is possible.
Wide spacing of the boreholes in a shallow (3000 to 6000 feet) producing formation so that the hydrocarbons may be efficiently produced presents a problem with the use of such templates. If angular deviation from the vertical does not begin until a point which is 1500 to 2000 feet toward such a shallow producing formation, little angular deviation can be achieved in the remaining distance to the shallow producing formation. It then becomes necessary to drill satellite wells with their attendent complications and expense in order to efficiently produce hydrocarbons from a shallow formation.